Thermoelements on a semiconductor base are known. They consist, for example, of two small semiconductor blocks of different conductivity type interconnected by a metal U-shaped element. When the exposed respective block ends are heated by the thermal radiation which is to be measured, a thermo-voltage is generated which may be tapped at the opposed respective block. This voltage is proportional to the temperature increase due to the converted radiation power. These thermoelements on a semiconductor base are actually relatively sensitive, but, as a result of their mass, they exhibit a thermal inertia which prevents them from following relatively rapid changes in intensity in the oncoming radiation.
The thermovoltage emitted by an individual thermoelement, which lies in the region of millivolts, requires a high amplification to raise it to a signal level required for display, or further measured value processing. Since a high d.c. voltage amplification involves a number of practical problems, frequently multiple thermoelements consisting of series-connected individual elements are employed in thermoelements; in such an arrangement, the output voltage corresponds to the sum of all the individual element thermovoltages. It is, however, necessary for each of the individual elements to receive the same radiation power if the temperature of a homogeneous radiation source is to be measured. In practice, this is very difficult if not impossible to achieve, particularly in the case of radiation pyrometers, in which the object to be measured is to be portrayed on the relatively large receiver surface of a multiple thermoelement.